ASTM E203-24
(Test Method)Standard Test Method for Water Using Volumetric Karl Fischer Titration
Standard Test Method for Water Using Volumetric Karl Fischer Titration
SIGNIFICANCE AND USE
4.1 Titration techniques using KF reagent are one of the most widely used for the determination of water.
4.2 Although the volumetric KF titration can determine low levels of water, it is generally accepted that coulometric KF titrations (see Test Method E1064) are more accurate for routine determination of very low levels of water. As a general rule, if samples routinely contain water concentrations of 500 mg/kg or less, the coulometric technique should be considered.
4.3 Applications can be subdivided into two sections: (1) organic and inorganic compounds, in which water may be determined directly, and (2) compounds, in which water cannot be determined directly, but in which interferences may be eliminated by suitable chemical reactions or modifications of the procedure. Further discussion of interferences is included in Section 5 and Appendix X2.
4.4 Water can be determined directly in the presence of the following types of compounds:
Organic Compounds
Acetals
Ethers
Acids (Note 1)
Halides
Acyl halides
Hydrocarbons (saturated and unsaturated)
Alcohols
Ketones, stable (Note 4)
Aldehydes, stable (Note 2)
Nitriles
Amides
Orthoesters
Amines, weak (Note 3)
Peroxides (hydro, dialkyl)
Anhydrides
Sulfides
Disulfides
Thiocyanates
Esters
Thioesters
Inorganic Compounds
Acids (Note 5)
Cupric oxide
Acid oxides (Note 6)
Desiccants
Aluminum oxides
Hydrazine sulfate
Anhydrides
Salts of organic and inorganic acids (Note 6)
Barium dioxide
Calcium carbonate
Note 1: Some acids, such as formic, acetic, and adipic acid, are slowly esterified. When using pyridine-free reagents, commercially available buffer solutions can be added to the sample prior to titration. With formic acid, it may be necessary to use methanol-free solvents and titrants (1).4
Note 2: Examples of stable aldehydes are formaldehyde, sugars, chloral, etc. Formaldehyde polymers cont...
SCOPE
1.1 This test method is intended as a general guide for the application of the volumetric Karl Fischer (KF) titration for determining free water and water of hydration in most solid or liquid organic and inorganic compounds. This test method is designed for use with automatic titration systems capable of determining the KF titration end point potentiometrically; however, a manual titration method for determining the end point visually is included as Appendix X1. Samples that are gaseous at room temperature are not covered (see Appendix X4). This test method covers the use of pyridine-free KF reagents for determining water by the volumetric titration. Determination of water using KF coulometric titration is not discussed. By proper choice of the sample size, KF reagent concentration and apparatus, this test method is suitable for measurement of water over a wide concentration range, that is, parts per million to pure water.
1.2 The values stated in SI units are to be regarded as standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific warnings are given in 3.1.
1.4 Review the current Safety Data Sheets (SDS) for detailed information concerning toxicity, first aid procedures, and safety precautions for chemicals used in this test procedure.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
- Status
- Published
- Publication Date
- 31-Dec-2023
- Technical Committee
- D16 - Aromatic, Industrial, Specialty and Related Chemicals
- Drafting Committee
- D16.04 - Instrumental Analysis
Relations
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Feb-2024
- Effective Date
- 15-Jul-2023
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Effective Date
- 01-Jan-2024
- Referred By
ASTM D4017-22 - Standard Test Method for Water in Paints and Paint Materials by Karl Fischer Method - Effective Date
- 01-Jan-2024
Overview
ASTM E203-24: Standard Test Method for Water Using Volumetric Karl Fischer Titration provides a comprehensive protocol for determining free water and water of hydration in most solid or liquid organic and inorganic compounds. Developed by ASTM International, this standard is widely adopted in laboratory and industrial settings for accurate water determination using the classic volumetric Karl Fischer (KF) titration method. The method accommodates both manual and automatic titration systems and supports the use of pyridine-free reagents to improve safety and adaptability. While it excels across a wide concentration range-from parts per million (ppm) to pure water-ASTM E203 is particularly valuable when routine analysis does not require the higher sensitivity of coulometric methods.
Key Topics
- Applicability: Suitable for a broad spectrum of materials, including both organic and inorganic substances, whether in liquid or solid form.
- KF Titration Process: Involves titrating a dissolved or dispersed sample with a KF reagent and detecting the endpoint potentiometrically or visually (manual titration guidance included in the appendix).
- Reagent Use: Addresses both pyridine and pyridine-free reagents. Pyridine-free formulations are generally favored for improved safety and stability.
- Sample Compatibility: Water can be directly determined in numerous compounds, such as ethers, acids, halides, aldehydes, alcohols, anhydrides, esters, amines, hydrocarbons, nitriles, and specific inorganic compounds like aluminum oxides, acid oxides, and desiccants.
- Measurement Range: Effective for water contents from very low ppm levels up to pure water, depending on appropriate choice of reagent, solvent, and apparatus.
- Precision and Sensitivity: The method delivers high repeatability and reproducibility, with precision estimates provided for various sample types and instrument configurations.
- Interference Management: The standard details common interferences (e.g., strong amines, aldehydes, ferric salts, mercaptans) and offers strategies to mitigate their effects via chemical modifications or alternative solvents.
Applications
- Chemical and Petrochemical Industry: Assessment of water in solvents, acids, hydrocarbons, lubricants, paint materials, and rubber additives.
- Pharmaceutical Manufacturing: Determination of water content in drugs, excipients, and intermediates, where accurate moisture content is imperative.
- Research and Development: Widely used in analytical labs for material characterization and quality control.
- Quality Assurance: Ensures compliance with product specifications and international standards by providing reliable data for process monitoring and batch certification.
Volumetric Karl Fischer titration is an essential analytical tool for professionals involved in moisture analysis, supporting industries to maintain product integrity, prevent spoilage, and meet regulatory requirements.
Related Standards
- ASTM E1064: Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration (recommended for samples with water concentrations of 500 mg/kg or less).
- ASTM D1364: Test Method for Water in Volatile Solvents (Karl Fischer Reagent Titration Method).
- ASTM D6304: Determination of Water in Petroleum Products by Coulometric Karl Fischer Titration.
- ASTM D890, D803, D1123, D4928: Specialized ASTM standards for determination of water in various chemical and industrial products.
Practical Value
Employing ASTM E203-24 ensures accurate, repeatable, and standardized water determination across diverse sample matrices, supporting both regulatory compliance and internal quality standards. The method’s adaptability to a wide range of sample types and concentrations makes it indispensable for laboratories and manufacturers, affirming its status as one of the most reliable volumetric titration techniques for moisture analysis globally.
Keywords: volumetric Karl Fischer titration, water determination, ASTM E203, pyridine-free reagent, laboratory water analysis, moisture content, organic compounds, inorganic compounds, quality control.
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Frequently Asked Questions
ASTM E203-24 is a standard published by ASTM International. Its full title is "Standard Test Method for Water Using Volumetric Karl Fischer Titration". This standard covers: SIGNIFICANCE AND USE 4.1 Titration techniques using KF reagent are one of the most widely used for the determination of water. 4.2 Although the volumetric KF titration can determine low levels of water, it is generally accepted that coulometric KF titrations (see Test Method E1064) are more accurate for routine determination of very low levels of water. As a general rule, if samples routinely contain water concentrations of 500 mg/kg or less, the coulometric technique should be considered. 4.3 Applications can be subdivided into two sections: (1) organic and inorganic compounds, in which water may be determined directly, and (2) compounds, in which water cannot be determined directly, but in which interferences may be eliminated by suitable chemical reactions or modifications of the procedure. Further discussion of interferences is included in Section 5 and Appendix X2. 4.4 Water can be determined directly in the presence of the following types of compounds: Organic Compounds Acetals Ethers Acids (Note 1) Halides Acyl halides Hydrocarbons (saturated and unsaturated) Alcohols Ketones, stable (Note 4) Aldehydes, stable (Note 2) Nitriles Amides Orthoesters Amines, weak (Note 3) Peroxides (hydro, dialkyl) Anhydrides Sulfides Disulfides Thiocyanates Esters Thioesters Inorganic Compounds Acids (Note 5) Cupric oxide Acid oxides (Note 6) Desiccants Aluminum oxides Hydrazine sulfate Anhydrides Salts of organic and inorganic acids (Note 6) Barium dioxide Calcium carbonate Note 1: Some acids, such as formic, acetic, and adipic acid, are slowly esterified. When using pyridine-free reagents, commercially available buffer solutions can be added to the sample prior to titration. With formic acid, it may be necessary to use methanol-free solvents and titrants (1).4 Note 2: Examples of stable aldehydes are formaldehyde, sugars, chloral, etc. Formaldehyde polymers cont... SCOPE 1.1 This test method is intended as a general guide for the application of the volumetric Karl Fischer (KF) titration for determining free water and water of hydration in most solid or liquid organic and inorganic compounds. This test method is designed for use with automatic titration systems capable of determining the KF titration end point potentiometrically; however, a manual titration method for determining the end point visually is included as Appendix X1. Samples that are gaseous at room temperature are not covered (see Appendix X4). This test method covers the use of pyridine-free KF reagents for determining water by the volumetric titration. Determination of water using KF coulometric titration is not discussed. By proper choice of the sample size, KF reagent concentration and apparatus, this test method is suitable for measurement of water over a wide concentration range, that is, parts per million to pure water. 1.2 The values stated in SI units are to be regarded as standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific warnings are given in 3.1. 1.4 Review the current Safety Data Sheets (SDS) for detailed information concerning toxicity, first aid procedures, and safety precautions for chemicals used in this test procedure. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
SIGNIFICANCE AND USE 4.1 Titration techniques using KF reagent are one of the most widely used for the determination of water. 4.2 Although the volumetric KF titration can determine low levels of water, it is generally accepted that coulometric KF titrations (see Test Method E1064) are more accurate for routine determination of very low levels of water. As a general rule, if samples routinely contain water concentrations of 500 mg/kg or less, the coulometric technique should be considered. 4.3 Applications can be subdivided into two sections: (1) organic and inorganic compounds, in which water may be determined directly, and (2) compounds, in which water cannot be determined directly, but in which interferences may be eliminated by suitable chemical reactions or modifications of the procedure. Further discussion of interferences is included in Section 5 and Appendix X2. 4.4 Water can be determined directly in the presence of the following types of compounds: Organic Compounds Acetals Ethers Acids (Note 1) Halides Acyl halides Hydrocarbons (saturated and unsaturated) Alcohols Ketones, stable (Note 4) Aldehydes, stable (Note 2) Nitriles Amides Orthoesters Amines, weak (Note 3) Peroxides (hydro, dialkyl) Anhydrides Sulfides Disulfides Thiocyanates Esters Thioesters Inorganic Compounds Acids (Note 5) Cupric oxide Acid oxides (Note 6) Desiccants Aluminum oxides Hydrazine sulfate Anhydrides Salts of organic and inorganic acids (Note 6) Barium dioxide Calcium carbonate Note 1: Some acids, such as formic, acetic, and adipic acid, are slowly esterified. When using pyridine-free reagents, commercially available buffer solutions can be added to the sample prior to titration. With formic acid, it may be necessary to use methanol-free solvents and titrants (1).4 Note 2: Examples of stable aldehydes are formaldehyde, sugars, chloral, etc. Formaldehyde polymers cont... SCOPE 1.1 This test method is intended as a general guide for the application of the volumetric Karl Fischer (KF) titration for determining free water and water of hydration in most solid or liquid organic and inorganic compounds. This test method is designed for use with automatic titration systems capable of determining the KF titration end point potentiometrically; however, a manual titration method for determining the end point visually is included as Appendix X1. Samples that are gaseous at room temperature are not covered (see Appendix X4). This test method covers the use of pyridine-free KF reagents for determining water by the volumetric titration. Determination of water using KF coulometric titration is not discussed. By proper choice of the sample size, KF reagent concentration and apparatus, this test method is suitable for measurement of water over a wide concentration range, that is, parts per million to pure water. 1.2 The values stated in SI units are to be regarded as standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific warnings are given in 3.1. 1.4 Review the current Safety Data Sheets (SDS) for detailed information concerning toxicity, first aid procedures, and safety precautions for chemicals used in this test procedure. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
ASTM E203-24 is classified under the following ICS (International Classification for Standards) categories: 71.040.40 - Chemical analysis. The ICS classification helps identify the subject area and facilitates finding related standards.
ASTM E203-24 has the following relationships with other standards: It is inter standard links to ASTM E203-23, ASTM D4672-24, ASTM E1064-23, ASTM D4815-22, ASTM D5008-22, ASTM D5983-21, ASTM D5798-21, ASTM D3218-07(2018), ASTM D1123-22a, ASTM D6304-20, ASTM E1417/E1417M-21e1, ASTM D4252-89(2017), ASTM D5501-20, ASTM E200-23, ASTM D4017-22. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
ASTM E203-24 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E203 − 24
Standard Test Method for
Water Using Volumetric Karl Fischer Titration
This standard is issued under the fixed designation E203; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
2.1 A list of existing ASTM Karl Fischer methods, their
1.1 This test method is intended as a general guide for the
applications to various products, and the sponsoring commit-
application of the volumetric Karl Fischer (KF) titration for
tees is given in Appendix X3.
determining free water and water of hydration in most solid or
liquid organic and inorganic compounds. This test method is
2.2 ASTM Standards:
designed for use with automatic titration systems capable of
D803 Test Methods for Testing Tall Oil
determining the KF titration end point potentiometrically;
D890 Test Method for Water in Liquid Pine Chemicals
however, a manual titration method for determining the end
D1123 Test Methods for Water in Engine Coolant Concen-
point visually is included as Appendix X1. Samples that are
trate by the Karl Fischer Reagent Method
gaseous at room temperature are not covered (see Appendix
D1193 Specification for Reagent Water
X4). This test method covers the use of pyridine-free KF
D1348 Test Methods for Moisture in Cellulose (Withdrawn
reagents for determining water by the volumetric titration.
2017)
Determination of water using KF coulometric titration is not
D1364 Test Method for Water in Volatile Solvents (Karl
discussed. By proper choice of the sample size, KF reagent
Fischer Reagent Titration Method)
concentration and apparatus, this test method is suitable for
D1533 Test Method for Water in Insulating Liquids by
measurement of water over a wide concentration range, that is,
Coulometric Karl Fischer Titration
parts per million to pure water.
D1568 Test Methods for Sampling and Chemical Analysis of
Alkylbenzene Sulfonates (Withdrawn 2023)
1.2 The values stated in SI units are to be regarded as
D1631 Test Method for Water in Phenol and Related Mate-
standard.
rials by the Iodine Reagent Method
1.3 This standard does not purport to address all of the
D2072 Test Method for Water in Fatty Nitrogen Compounds
safety concerns, if any, associated with its use. It is the
(Withdrawn 2007)
responsibility of the user of this standard to establish appro-
D2575 Methods of Testing Polymerized Fatty Acids (With-
priate safety, health, and environmental practices and deter-
drawn 2007)
mine the applicability of regulatory limitations prior to use.
D3277 Test Methods for Moisture Content of Oil-
Specific warnings are given in 3.1.
Impregnated Cellulosic Insulation (Withdrawn 2010)
1.4 Review the current Safety Data Sheets (SDS) for de-
D3401 Test Methods for Water in Halogenated Organic
tailed information concerning toxicity, first aid procedures, and
Solvents and Their Admixtures
safety precautions for chemicals used in this test procedure.
D4017 Test Method for Water in Paints and Paint Materials
1.5 This international standard was developed in accor- by Karl Fischer Method
D4672 Test Method for Polyurethane Raw Materials: Deter-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the mination of Water Content of Polyols
Development of International Standards, Guides and Recom- D4928 Test Method for Water in Crude Oils by Coulometric
mendations issued by the World Trade Organization Technical Karl Fischer Titration
Barriers to Trade (TBT) Committee. D5460 Test Method for Rubber Compounding Materials—
Water in Rubber Additives
1 2
This test method is under the jurisdiction of ASTM Committee D16 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Aromatic, Industrial, Specialty and Related Chemicals and is the direct responsi- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
bility of Subcommittee D16.04 on Instrumental Analysis. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Jan. 1, 2024. Published January 2024. Originally the ASTM website.
approved in 1962 as E203 – 62 T. Last previous edition approved in 2023 as The last approved version of this historical standard is referenced on
E203 – 23. DOI: 10.1520/E0203-24. www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E203 − 24
D5530 Test Method for Total Moisture of Hazardous Waste
Acyl halides Hydrocarbons (saturated and unsaturated)
Alcohols Ketones, stable (Note 4)
Fuel by Karl Fischer Titrimetry
Aldehydes, stable (Note 2) Nitriles
D6304 Test Method for Determination of Water in Petro-
Amides Orthoesters
leum Products, Lubricating Oils, and Additives by Cou-
Amines, weak (Note 3) Peroxides (hydro, dialkyl)
Anhydrides Sulfides
lometric Karl Fischer Titration
Disulfides Thiocyanates
D6809 Guide for Quality Control and Quality Assurance
Esters Thioesters
Procedures for Aromatic Hydrocarbons and Related Ma-
Inorganic Compounds
Acids (Note 5) Cupric oxide
terials
Acid oxides (Note 6) Desiccants
E180 Practice for Determining the Precision of ASTM
Aluminum oxides Hydrazine sulfate
Methods for Analysis and Testing of Industrial and Spe- Anhydrides Salts of organic and inorganic acids (Note 6)
Barium dioxide
cialty Chemicals (Withdrawn 2009)
Calcium carbonate
E1064 Test Method for Water in Organic Liquids by Coulo-
NOTE 1—Some acids, such as formic, acetic, and adipic acid, are slowly
metric Karl Fischer Titration
esterified. When using pyridine-free reagents, commercially available
buffer solutions can be added to the sample prior to titration. With formic
3. Summary of Test Method
acid, it may be necessary to use methanol-free solvents and titrants (1).
NOTE 2—Examples of stable aldehydes are formaldehyde, sugars,
3.1 The sample, containing a maximum of 100 mg of water,
chloral, etc. Formaldehyde polymers contain water as methylol groups.
is dissolved or dispersed in a suitable liquid and titrated with
This combined water is not titrated. Addition of an excess of NaOCH in
KF reagent, which consists of iodine, sulfur dioxide, organic
methanol permits release and titration of this combined water, after
base, and a solvent (typically an alcohol, such as methanol,
approximate neutralization of excess base with acetic acid (see Note 9).
NOTE 3—Weak amines are considered to be those with K value
ethylene glycol, or 2-methoxyethanol). The titration end point
b
−5
<2.4 × 10 .
is determined potentiometrically with a platinum electrode
NOTE 4—Examples of stable ketones are diisopropyl ketone, camphor,
which senses a sharp change in cell resistance when the iodine
benzophenone, benzil, dibenzolacetone, etc.
is reduced by sulfur dioxide in the presence of water.
NOTE 5—Sulfuric acid up to a concentration of 92 % may be titrated
(Warning—KF reagent contains four toxic compounds,
directly; for higher concentrations see Note 13.
NOTE 6—Compounds subject to oxidation-reduction reactions in an
namely, iodine, sulfur dioxide, other organic bases, and metha-
iodine-iodide system interfere.
nol or glycol ether. The reagent should be dispensed in a
well-ventilated area. Care must be exercised to avoid inhala-
5. Interferences
tion of the reagent or direct contact of the reagent with the
5.1 Condensation and oxidation-reduction reactions cause
skin.)
interference in this titrimetric method. Also, a number of
3.2 The general equation to this reaction is as follows:
substances and classes of compounds interfere in the determi-
H O1I 1SO 1R'OH13 RN.~RNH!SO R'12~RNH!I (1)
nation of water by this method. Complete descriptions may be
2 2 2 4
found in the literature (2).
where:
5.2 Interferences of many classes of compounds can be
RN = an organic base, and
eliminated by chemical reactions to form inert compounds
R'OH = alcohol.
prior to titration. The following are in this category:
4. Significance and Use
Aldehydes and ketones, active (Note 7)
Amines, strong (Note 8)
4.1 Titration techniques using KF reagent are one of the
Ammonia (Note 9)
most widely used for the determination of water. Ferric salts (Note 10)
Hydrazine derivatives (Note 9)
4.2 Although the volumetric KF titration can determine low
Hydroxylamine salts (Note 11)
Mercaptans (Note 12)
levels of water, it is generally accepted that coulometric KF
Sodium methylate (Note 9)
titrations (see Test Method E1064) are more accurate for
Sulfuric acid (Note 13)
routine determination of very low levels of water. As a general
Thioacids (Note 12)
Thiourea (Note 12)
rule, if samples routinely contain water concentrations of 500
mg/kg or less, the coulometric technique should be considered.
NOTE 7—Use ethylene glycol monomethylether, ethylene glycol, ben-
zyl alcohol or dimethylformamide in place of the methanol solvent and
4.3 Applications can be subdivided into two sections: (1)
use a methanol-free titrant (1). The cyanhydrin reaction may be used to
organic and inorganic compounds, in which water may be
eliminate the interference (2).
determined directly, and (2) compounds, in which water cannot
NOTE 8—Strong amines are considered to be those with K value
b
−5
>2.4 × 10 . Use salicylic acid-methanol solution (Section 7). Glacial
be determined directly, but in which interferences may be
acetic acid is applicable in certain cases.
eliminated by suitable chemical reactions or modifications of
NOTE 9—Addition of acetic acid eliminates the interference.
the procedure. Further discussion of interferences is included
NOTE 10—Ferric fluoride does not interfere. Reaction with
in Section 5 and Appendix X2.
8-hydroxyquinoline is reported to eliminate this interference (3).
NOTE 11—The two component reagent methods should be used and 1
4.4 Water can be determined directly in the presence of the
mL of sulfuric acid is added to the solvent prior to titration (Note 15).
following types of compounds:
Organic Compounds
Acetals Ethers
The boldface numbers in parentheses refer to the list of references at the end of
Acids (Note 1) Halides
this test method.
E203 − 24
NOTE 12—Olefin addition reaction eliminates interferences (2). Oxida-
Litres of Diluent to Add/litre of
Desired Strength, mg H O/mL
tion with neutral iodine solution eliminates the interference of mercaptans
6 mg/mL KF reagent
(4). 3 0.85
2 1.6
NOTE 13—Addition of 8 mL of 1 + 1 pyridine-dioxane/1 g of
1 3.2
sample maintaining a homogeneous solution throughout the titration.
0.5 5.7
5.3 If there is a question of compounds listed in 5.2 causing
7.3.2.3 These dilute solutions cannot be prepared by simple
an interference, the recovery of spiked additions of water to the
proportion, since water added with the diluent must be ac-
sample matrix should be checked.
counted for. The volumes to add, indicated above, are calcu-
5.4 Many materials react stoichiometrically with KF re-
lated assuming the diluent contains 0.05 % water.
agent. When their concentration is known, suitable corrections
7.4 Water Standard (1 mL = 1 mg H O)—This solution can
can be applied. A list of such materials is given in Appendix
be stored conveniently in a bottle with rubber cap and portions
X2.
removed with a hypodermic syringe. Single use standards
stored in ampoules are also acceptable for use.
6. Apparatus
7.5 Sodium Tartrate Dihydrate—Grind certified material
6.1 Karl Fischer Volumetric Titrator, consisting of a titra-
(water content 15.61 % to 15.71 %) to a fine powder (prefer-
tion cell, dual platinum electrode, magnetic stirrer, dispensing
ably overnight in a sealed ball mill) and store the ground
buret and control unit. Many manufacturers of general purpose
material in a stoppered bottle. If doubt exists as to its water
laboratory titrators offer optional accessories that allow their
content, dry a 2 g to 3 g sample in an oven at 155 °C 6 5 °C
instrument to perform KF titrations.
to constant weight (min 4 h). (See Note 16.)
7. Reagents
7.6 Solvents:
7.1 Purity of Reagents—Use reagent grade chemicals in all 7.6.1 Acetic Acid, glacial.
tests. Unless otherwise indicated, all reagents shall conform to 7.6.2 Ethylene Glycol Monomethyl Ether, maximum 0.1 %
the specifications of the Committee on Analytical Reagents of water. (See Note 1.)
the American Chemical Society where such specifications are 7.6.3 Methanol, max 0.15 mass % water. (See Note 1.)
available. Other grades may be used, provided it is first
7.7 Solvents, Mixed—In addition to the single solvents (7.6),
ascertained that the reagent is of sufficiently high purity to
the following mixed solvents are useful for dissolving various
permit its use without lessening the accuracy of the determi-
samples:
nation.
7.7.1 Methanol—Chloroform (1 + 3)—Mix 1 volume of
7.2 Purity of Water—Unless otherwise indicated, references
methanol with 3 volumes of chloroform. Use for liquid
to water shall mean reagent water as defined by Type I or II of
petroleum products.
Specification D1193.
7.7.2 Methanol—Salicyclic Acid—Dissolve 150 g of salicy-
clic acid in 1 L of methanol. Use for amines.
7.3 Karl Fischer Reagents—Pyridine-free formulations are
available.
7.8 Sulfur Dioxide, anhydrous grade. (See Note 1.)
7.3.1 Pyridine-Free Karl Fischer Titrant—Typically con-
sists of a mixture of an organic base, sulfur dioxide and iodine
8. Drying of Solvents
dissolved in a solvent such as methanol or 2-methoxyethanol.
8.1 If it is necessary to prepare dry solvents in the
Reagents with titers of 1.00 mg H O/mL, 2.00 mg H O/mL,
2 2
laboratory, the following three methods can be used:
and 5.00 mg H O/mL can be commercially obtained.
8.1.1 Azeotropic Distillation Using Benzene, to reduce the
7.3.2 Pyridine-Free Karl Fischer Solvent—Anhydrous
moisture to 0.05 %. Add 1 volume of benzene to 19 volumes of
methanol is the most frequently used solvent, however, other
ethylene glycol monomethyl ether and distill. Discard the first
alcohols including glycols and glycol ethers are used. Some
5 % and use the dry residual 95 %.
commercially available solvents also contain an organic base
8.1.2 Molecular Sieves—Solvents other than methanol may
and sulfur dioxide.
be dried to a moisture content of 0.05 % by passing upward
7.3.2.1 Karl Fischer Reagent (Ethylene Glycol Monomethyl
through a molecular sieve column, using 1 part molecular sieve
Solution, Stabilized, 1 mL = 6 mg H O).
per 10 parts of solvent.
7.3.2.2 Karl Fischer Reagent, Dilute—Prepare more dilute
solutions of the KF reagent by diluting with the proper solvent
9. End Point Detection
as follows:
9.1 There are many commercial titration assemblies on the
market that are specifically designed for performing volumetric
Automatic volumetric titrators specifically designed for KF determinations are
type KF titrations. All that is required of these units is pressing
manufactured by many different companies. Models are available from Metrohm,
a “start titration” or “start” key on the instrument keyboard just
Mettler, Photovolt, Mitsubishi, and others.
prior to or after the sample has been added to the titration cell.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, American Chemical Society, Washington,
End point detection is automatic and the amount of water in the
DC. For suggestions on the testing of reagents not listed by the American Chemical
sample is calculated once the operator enters the sample weight
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
into the instrument’s memory. The method for color end point
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
copeial Convention, Inc. (USPC), Rockville, MD. detection is given in Appendix X1.
E203 − 24
10. Procedure for Soluble Materials, Either Liquid or
Water
Sodium Tartrate Water-in-Methanol,
Equivalent F, Water, mg
Solid
Dihydrate, g Standard, mL
mg/mL
10.1 Pipet 25 mL to 50 mL of the selected solvent into the 0.5 2.5–10 0.015–0.060 2.5–10
1 5–20 0.30–0.12 5–20
titration cell. Titrate the water in the solvent with KF reagent
2 10–40 0.06–0.24 10–40
according to the instrument manufacturer’s instructions. The
5 25–100 0.15–0.6 .
KF reagent that is used should be of appropriate titer as
11.2 Pipet 25 mL to 50 mL of methanol or appropriate
determined by the amount of water anticipated in the sample
solvent to a clean, dry titration cell and pretitrate according to
(see 10.2).
the instrument manufacturer’s instructions.
10.2 Weigh or pipet a sample containing an anticipated
11.3 Transfer the selected standard to the pretitrated solvent.
water content that will give a fast and accurate titration. KF
11.3.1 Weigh, to the nearest 0.0001 g, the indicated amount
instrument operation manuals typically list suggested sample
of water from a suitable weighing pipet, hypodermic syringe,
sizes, however, Table 1 also can be used as a guideline for
or other device, or
sample sizes of the three most common titrant titers. Keep in
mind that very small sample amounts may be difficult to
11.3.2 Transfer the weighed sodium tartrate dihydrate by
accurately weigh and transfer, whereas, very large sample
means of a dry spatula, dipping the spatula into the alcohol to
amounts may result in incomplete miscibility with the chosen
ensure removal of any adhering tartrate (Note 16), or
solvent.
11.3.3 Use a hypodermic syringe of suitable capacity to
transfer the standard water-in-methanol solution to the titration
NOTE 14—The KF technique described here is sometimes referred to as
the “one component” method because all the reagents are in the titrant, flask.
and the solvent is used basically as a medium to dissolve the sample.
There is also a “two component” KF volumetric titration in which the NOTE 16—To facilitate transferral of the tartrate to vessels having
titrant contains the usual reagents, but the solvent also contains sulfur constricted openings or narrow necks, a spatula with the tip bent at a right
angle to the handle is satisfactory. If the tartrate is used for standardizing
dioxide and a base. There are advantages to the two component system
since strongly basic or acid samples can overcome the buffering capacity Karl Fischer reagent for use with samples containing more than 1 % water,
a bias may exist which has been described in Ref (7).
of the single component system and cause the pH of the reaction mixture
to shift from the optimum range. The two component system provides
11.4 Titrate with KF reagent to the instrument manufactur-
initial sample buffering capacity in the solvent which may provide a faster
er’s instructions.
reaction time. Rapid end point determination also can provide more
accurate measurement of trace water concentrations. Two component
11.5 Calculation—Calculate the water equivalent, E, of the
reagents, however, are more susceptible to side reaction from noncom-
KF reagent, in milligrams per millilitre, as follows: Water as
plexed sulfur dioxide than single component systems (5).
NOTE 15—The range of water indicated is for macro titrations.
Standard:
Considerably smaller amounts of water can be determined precisely on a
G
micro scale. For example, less than 300 μg of water were titrated in 1 mL
F 5 1000 × (3)
A
samples of benzene by a micro amperometric technique (6)
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E203 − 23 E203 − 24
Standard Test Method for
Water Using Volumetric Karl Fischer Titration
This standard is issued under the fixed designation E203; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method is intended as a general guide for the application of the volumetric Karl Fischer (KF) titration for determining
free water and water of hydration in most solid or liquid organic and inorganic compounds. This test method is designed for use
with automatic titration systems capable of determining the KF titration end point potentiometrically; however, a manual titration
method for determining the end point visually is included as Appendix X1. Samples that are gaseous at room temperature are not
covered (see Appendix X4). This test method covers the use of both pyridine and pyridine-free KF reagents for determining water
by the volumetric titration. Determination of water using KF coulometric titration is not discussed. By proper choice of the sample
size, KF reagent concentration and apparatus, this test method is suitable for measurement of water over a wide concentration
range, that is, parts per million to pure water.
1.2 The values stated in SI units are to be regarded as standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. Specific warnings are given in 3.1 and 7.3.3.
1.4 Review the current Safety Data Sheets (SDS) for detailed information concerning toxicity, first aid procedures, and safety
precautions for chemicals used in this test procedure.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 A list of existing ASTM Karl Fischer methods, their applications to various products, and the sponsoring committees is given
in Appendix X3.
2.2 ASTM Standards:
D803 Test Methods for Testing Tall Oil
D890 Test Method for Water in Liquid Pine Chemicals
D1123 Test Methods for Water in Engine Coolant Concentrate by the Karl Fischer Reagent Method
This test method is under the jurisdiction of ASTM Committee D16 on Aromatic, Industrial, Specialty and Related Chemicals and is the direct responsibility of
Subcommittee D16.04 on Instrumental Analysis.
Current edition approved July 15, 2023Jan. 1, 2024. Published August 2023January 2024. Originally approved in 1962 as E203 – 62 T. Last previous edition approved
in 20162023 as E203 – 16.E203 – 23. DOI: 10.1520/E0203-23.10.1520/E0203-24.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E203 − 24
D1193 Specification for Reagent Water
D1348 Test Methods for Moisture in Cellulose (Withdrawn 2017)
D1364 Test Method for Water in Volatile Solvents (Karl Fischer Reagent Titration Method)
D1533 Test Method for Water in Insulating Liquids by Coulometric Karl Fischer Titration
D1568 Test Methods for Sampling and Chemical Analysis of Alkylbenzene Sulfonates (Withdrawn 2023)
D1631 Test Method for Water in Phenol and Related Materials by the Iodine Reagent Method
D2072 Test Method for Water in Fatty Nitrogen Compounds (Withdrawn 2007)
D2575 Methods of Testing Polymerized Fatty Acids (Withdrawn 2007)
D3277 Test Methods for Moisture Content of Oil-Impregnated Cellulosic Insulation (Withdrawn 2010)
D3401 Test Methods for Water in Halogenated Organic Solvents and Their Admixtures
D4017 Test Method for Water in Paints and Paint Materials by Karl Fischer Method
D4672 Test Method for Polyurethane Raw Materials: Determination of Water Content of Polyols
D4928 Test Method for Water in Crude Oils by Coulometric Karl Fischer Titration
D5460 Test Method for Rubber Compounding Materials—Water in Rubber Additives
D5530 Test Method for Total Moisture of Hazardous Waste Fuel by Karl Fischer Titrimetry
D6304 Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl
Fischer Titration
D6809 Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
E180 Practice for Determining the Precision of ASTM Methods for Analysis and Testing of Industrial and Specialty Chemicals
(Withdrawn 2009)
E1064 Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
3. Summary of Test Method
3.1 The sample, containing a maximum of 100 mg of water, is dissolved or dispersed in a suitable liquid and titrated with KF
reagent, which consists of iodine, sulfur dioxide, organic base, and a solvent (typically an alcohol, such as methanol, ethylene
glycol, or 2-methoxyethanol). The titration end point is determined potentiometrically with a platinum electrode which senses a
sharp change in cell resistance when the iodine is reduced by sulfur dioxide in the presence of water. (Warning—KF reagent
contains four toxic compounds, namely, iodine, sulfur dioxide, pyridine or other organic bases, and methanol or glycol ether. The
reagent should be dispensed in a well-ventilated area. Care must be exercised to avoid inhalation of the reagent or direct contact
of the reagent with the skin.)
3.2 The general equation to this reaction is as follows:
H O1I 1SO 1R'OH13 RN.~RNH!SO R'12~RNH!I (1)
2 2 2 4
where:
RN = an organic base such as pyridine, and
RN = an organic base, and
R'OH = alcohol.
4. Significance and Use
4.1 Titration techniques using KF reagent are one of the most widely used for the determination of water.
4.2 Although the volumetric KF titration can determine low levels of water, it is generally accepted that coulometric KF titrations
(see Test Method E1064) are more accurate for routine determination of very low levels of water. As a general rule, if samples
routinely contain water concentrations of 500 mg/kg or less, the coulometric technique should be considered.
4.3 Applications can be subdivided into two sections: (1) organic and inorganic compounds, in which water may be determined
directly, and (2) compounds, in which water cannot be determined directly, but in which interferences may be eliminated by
suitable chemical reactions or modifications of the procedure. Further discussion of interferences is included in Section 5 and
Appendix X2.
The last approved version of this historical standard is referenced on www.astm.org.
E203 − 24
4.4 Water can be determined directly in the presence of the following types of compounds:
Organic Compounds
Acetals Ethers
Acids (Note 1) Halides
Acyl halides Hydrocarbons (saturated and unsaturated)
Alcohols Ketones, stable (Note 4)
Aldehydes, stable (Note 2) Nitriles
Amides Orthoesters
Amines, weak (Note 3) Peroxides (hydro, dialkyl)
Anhydrides Sulfides
Disulfides Thiocyanates
Esters Thioesters
Inorganic Compounds
Acids (Note 5) Cupric oxide
Acid oxides (Note 6) Desiccants
Aluminum oxides Hydrazine sulfate
Anhydrides Salts of organic and inorganic acids (Note 6)
Barium dioxide
Calcium carbonate
NOTE 1—Some acids, such as formic, acetic, and adipic acid, are slowly esterified. For high accuracy with pyridine-based reagents, use 30 % to 50 %
pyridine in methanol as the solvent. When using pyridine-free reagents, commercially available buffer solutions can be added to the sample prior to
titration. With formic acid, it may be necessary to use methanol-free solvents and titrants (1).
NOTE 2—Examples of stable aldehydes are formaldehyde, sugars, chloral, etc. Formaldehyde polymers contain water as methylol groups. This combined
water is not titrated. Addition of an excess of NaOCH in methanol permits release and titration of this combined water, after approximate neutralization
of excess base with acetic acid (see Note 9).
−5
NOTE 3—Weak amines are considered to be those with K value <2.4 × 10 .
b
NOTE 4—Examples of stable ketones are diisopropyl ketone, camphor, benzophenone, benzil, dibenzolacetone, etc.
NOTE 5—Sulfuric acid up to a concentration of 92 % may be titrated directly; for higher concentrations see Note 13.
NOTE 6—Compounds subject to oxidation-reduction reactions in an iodine-iodide system interfere.
5. Interferences
5.1 Condensation and oxidation-reduction reactions cause interference in this titrimetric method. Also, a number of substances and
classes of compounds interfere in the determination of water by this method. Complete descriptions may be found in the literature
(2).
5.2 Interferences of many classes of compounds can be eliminated by chemical reactions to form inert compounds prior to
titration. The following are in this category:
Aldehydes and ketones, active (Note 7)
Amines, strong (Note 8)
Ammonia (Note 9)
Ferric salts (Note 10)
Hydrazine derivatives (Note 9)
Hydroxylamine salts (Note 11)
Mercaptans (Note 12)
Sodium methylate (Note 9)
Sulfuric acid (Note 13)
Thioacids (Note 12)
Thiourea (Note 12)
NOTE 7—This interference may be reduced by use of pyridine rather than methanol as solvent for the same or by the use of KF reagent and solvent
prepared with ethylene glycol monomethyl ether in place of methanol. For pyridine-free reagents, use ethylene glycol Use ethylene glycol
monomethylether, ethylene glycol, benzyl alcohol or dimethylformamide in place of the methanol solvent and use a methanol-free titrant (1). The
cyanhydrin reaction may be used to eliminate the interference (2).
The boldface numbers in parentheses refer to the list of references at the end of this test method.
E203 − 24
−5
NOTE 8—Strong amines are considered to be those with K value >2.4 × 10 . Use salicylic acid-methanol solution (Section 7). Glacial acetic acid is
b
applicable in certain cases.
NOTE 9—Addition of acetic acid eliminates the interference.
NOTE 10—Ferric fluoride does not interfere. Reaction with 8-hydroxyquinoline is reported to eliminate this interference (3).
NOTE 11—With pyridine-based reagent, add 1 mol/L SOThe in 1 + 1 pyridine-methanol or spent KF reagent. With pyridine-free reagents, the two
component reagent methods should be used and 1 mL of sulfuric acid is added to the solvent prior to titration (Note 15).
NOTE 12—Olefin addition reaction eliminates interferences (2). Oxidation with neutral iodine solution eliminates the interference of mercaptans (4).
NOTE 13—Sulfuric acid, above 92 %. Add the sample (10 g) to a large excess of pyridine (35 mL), swirl to dissolve precipitate, and titrate. Addition of
8 mL of 1 + 1 pyridine-dioxane/1 g of sample also is satisfactory, maintaining sample maintaining a homogeneous solution throughout the titration.
5.3 If there is a question of compounds listed in 5.2 causing an interference, the recovery of spiked additions of water to the sample
matrix should be checked.
5.4 Many materials react stoichiometrically with KF reagent. When their concentration is known, suitable corrections can be
applied. A list of such materials is given in Appendix X2.
6. Apparatus
6.1 Karl Fischer Volumetric Titrator, consisting of a titration cell, dual platinum electrode, magnetic stirrer, dispensing buret and
control unit. Many manufacturers of general purpose laboratory titrators offer optional accessories that allow their instrument to
perform KF titrations.
7. Reagents
7.1 Purity of Reagents—Use reagent grade chemicals in all tests. Unless otherwise indicated, all reagents shall conform to the
specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available.
Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without
lessening the accuracy of the determination.
7.2 Purity of Water—Unless otherwise indicated, references to water shall mean reagent water as defined by Type I or II of
Specification D1193.
7.3 Karl Fischer Reagents—Traditionally, pyridine was the organic base used in KF reagents. Pyridine-free formulations,
however, are available now and are preferred by most KF instrument manufacturers for use with their equipment. These reagents
are less toxic, less odorous, and more stable than those containing pyridine. The use of pyridine-free reagents is recommended
whenever possible.Pyridine-free formulations are available.
7.3.1 Pyridine-Free Karl Fischer Titrant—Typically consists of a mixture of an organic base, sulfur dioxide and iodine dissolved
in a solvent such as methanol or 2-methoxyethanol. Reagents with titers of 1.00, 2.00, 1.00 mg H O/mL, 2.00 mg H O/mL, and
2 2
5.00 mg H O/mL can be commercially obtained.
7.3.2 Pyridine-Free Karl Fischer Solvent—Anhydrous methanol is the most frequently used solvent, however, other alcohols
including glycols and glycol ethers are used. Some commercially available solvents also contain an organic base and sulfur dioxide.
7.3.2 Pyridine-Free Karl Fischer Reagent Containing Pyridine—Solvent—The KF reagent may be either prepared in the
laboratory or purchased. Two types of reagent are commonly used. Directions for preparing these and diluting if necessary, along
with commercial sources of supply, are as follows: (Anhydrous methanol is the most frequently used solvent, however, other
alcohols including glycols and glycol ethers are used. Some commercially available solvents also contain an organic base and
sulfur dioxide.Warning—Follow standard precautions for handling toxic gases in preparing the reagents (1) or (2) as described
Automatic volumetric titrators specifically designed for KF determinations are manufactured by many different companies. Models are available from Metrohm, Mettler,
Photovolt, Mitsubishi, and others.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
E203 − 24
in 7.3.3.1 and 7.3.3.2. Carry out all operations in a hood. Wear rubber gloves and a face shield when handling pyridine and sulfur
dioxide and when mixing chemicals. Special precautions must be observed when dispensing sulfur dioxide to prevent drawback
of the solution into the gas cylinder, which might cause an explosion. This is best accomplished by placing a trap in the line
between the gas cylinder and absorption vessel.)
7.3.2.1 Karl Fischer Reagent (Ethylene Glycol Monomethyl Ether Solution, 1 mL = 6 mg HStabilized, O) (2)—For each litre of
solution, dissolve 133 g 6 1 g iodine in 425 mL 6 5 mL of pyridine in a dry glass-stoppered bottle. Add 425 mL 6 5 mL of
ethylene glycol monomethyl ether. Cool to below 4 °C in an ice bath. Bubble 102 g to 105 g of gaseous sulfur dioxide (SO1 mL = 6
mg H ) into the cooled mixture. Determine the amount of SOO). added by the change in weight of the SO cylinder or the increase
2 2 2
in volume (about 70 mL) of the reagent mixture. Alternatively, add about 70 mL of freshly drawn liquid SO in small increments.
Mix well and set aside for at least 12 h before using. (Warning—see 7.3.3.)
7.3.3.2 Karl Fischer Reagent (Methanol Solution, 1 mL = 6 mg H O)—For each litre of solution, dissolve 133 g 6 1 g of iodine
in 425 mL 6 5 mL of pyridine in a dry, glass-stoppered bottle. Add 425 mL 6 5 mL of methanol. Cool the mixture in an ice bath
to below 4 °C. Bubble 102 g to 105 g of gaseous sulfur dioxide (SO ) into the cooled mixture. Determine the amount of SO added
2 2
by the change in weight of the SO cylinder or the increase in volume (about 70 mL) of the reagent mixture. Alternatively, add
about 70 mL of freshly drawn liquid SO in small increments. Mix well and set aside for at least 12 h before using. (Warning—see
7.3.3.)
7.3.3.3 Karl Fischer Reagent (Ethylene Glycol Monomethyl Solution, Stabilized, 1 mL = 6 mg H O).
7.3.2.2 Karl Fischer Reagent, Dilute—Prepare more dilute solutions of the KF reagent by diluting with the proper solvent as
follows:
Litres of Diluent to Add/litre of
Desired Strength, mg H O/mL
6 mg/mL KF reagent
3 0.85
2 1.6
1 3.2
0.5 5.7
These dilute solutions cannot be prepared by simple proportion, since water added with the diluent must be accounted for. The
volumes to add, indicated above, are calculated assuming the diluent contains 0.05 % water.
7.3.2.3 These dilute solutions cannot be prepared by simple proportion, since water added with the diluent must be accounted for.
The volumes to add, indicated above, are calculated assuming the diluent contains 0.05 % water.
7.4 Water Standard (1 mL = 1 mg H O)—This solution can be stored conveniently in a bottle with rubber cap and portions
removed with a hypodermic syringe. Single use standards stored in ampoules are also acceptable for use.
7.5 Sodium Tartrate Dihydrate—Grind certified material (water content 15.61 % to 15.71 %) to a fine powder (preferably
overnight in a sealed ball mill) and store the ground material in a stoppered bottle. If doubt exists as to its water content, dry a
2 g to 3 g sample in an oven at 155 °C 6 5 °C to constant weight (min 4 h). (See Note 16.)
7.6 Solvents:
7.6.1 Acetic Acid, glacial.
7.6.2 Ethylene Glycol Monomethyl Ether, maximum 0.1 % water. (See Note 1.)
7.6.3 Methanol, max 0.15 mass % water. (See Note 1.)
7.6.4 Pyridine, maximum 0.1 % water. (See Note 1.)
7.7 Solvents, Mixed—In addition to the single solvents (7.6), the following mixed solvents are useful for dissolving various
samples:
7.7.1 Methanol—Chloroform (1 + 3)—Mix 1 volume of methanol with 3 volumes of chloroform. Use for liquid petroleum
products.
E203 − 24
7.7.2 Methanol—Salicyclic Acid—Dissolve 150 g of salicyclic acid in 1 L of methanol. Use for amines.
7.7.3 Pyridine—Ethylene Glycol (1 + 4)—Mix 1 volume of pyridine with 4 volumes of ethylene glycol. Use for compounds
containing carbonyl groups.
7.7.4 Pyridine—Methanol (1 + 4)—Mix 1 volume of pyridine with 4 volumes of methanol. Use for organic acids.
7.8 Sulfur Dioxide, anhydrous grade. (See Note 1 and 7.3.3.)
8. Drying of Solvents
8.1 If it is necessary to prepare dry solvents in the laboratory, the following three methods can be used:
8.1.1 Azeotropic Distillation Using Benzene, to reduce the moisture to 0.05 %. Add 1 volume of benzene to 19 volumes of
pyridine, ethylene glycol monomethyl ether, or mixtures thereof, ether and distill. Discard the first 5 % and use the dry residual
95 %.
8.1.2 Molecular Sieves—Solvents other than methanol may be dried to a moisture content of 0.05 % by passing upward through
a molecular sieve column, using 1 part molecular sieve per 10 parts of solvent.
9. End Point Detection
9.1 There are many commercial titration assemblies on the market that are specifically designed for performing volumetric type
KF titrations. All that is required of these units is pressing a “start titration” or “start” key on the instrument keyboard just prior
to or after the sample has been added to the titration cell. End point detection is automatic and the amount of water in the sample
is calculated once the operator enters the sample weight into the instrument’s memory. The method for color end point detection
is given in Appendix X1.
10. Procedure for Soluble Materials, Either Liquid or Solid
10.1 Pipet 25 mL to 50 mL of the selected solvent into the titration cell. Titrate the water in the solvent with KF reagent according
to the instrument manufacturer’s instructions. The KF reagent that is used should be of appropriate titer as determined by the
amount of water anticipated in the sample (see 10.2).
10.2 Weigh or pipet a sample containing an anticipated water content that will give a fast and accurate titration. KF instrument
operation manuals typically list suggested sample sizes, however, Table 1 also can be used as a guideline for sample sizes of the
three most common titrant titers. Keep in mind that very small sample amounts may be difficult to accurately weigh and transfer,
whereas, very large sample amounts may result in incomplete miscibility with the chosen solvent.
NOTE 14—The KF technique described here is sometimes referred to as the “one component” method because all the reagents are in the titrant, and the
solvent is used basically as a medium to dissolve the sample. There is also a “two component” KF volumetric titration in which the titrant contains the
usual reagents, but the solvent also contains sulfur dioxide and a base. There are advantages to the two component system since strongly basic or acid
samples can overcome the buffering capacity of the single component system and cause the pH of the reaction mixture to shift from the optimum range.
The two component system provides initial sample buffering capacity in the solvent which may provide a faster reaction time. Rapid end point
determination also can provide more accurate measurement of trace water concentrations. Two component reagents, however, are more susceptible to side
reaction from noncomplexed sulfur dioxide than single component systems (5).
NOTE 15—The range of water indicated is for macro titrations. Considerably smaller amounts of water can be determined precisely on a micro scale. For
TABLE 1 Recommended Sample Amount
1 mg H O/mL 2 mg H O/mL 5 mg H O/mL
2 2 2
Water Content
Titrant Titrant Titrant
100 % . . 25 mg to 50 mg
10 % 25 mg to 50 mg 25 mg to 100 mg 50 mg to 250 mg
1 % 0.1 g to 0.5 g 0.2 g to 11 g 0.5 g to 2.5 g
0.1 % 1 g to 5 g 2 g to 10 g 5 g to 20 g
100 ppm 5 g to 10 g 10 g to 20 g .
25 ppm >20 g . .
-------------------
...
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